The present invention relates to an apparatus for cutting by means of a high pressure fluid jet intended for cutting sheet-like materials, such as plastics, paper, leather, rubber, etc. and composite materials in the form of layers of fibres and more particularly synthetic fibres, such as glass, carbon or aromatic polyamide fibres, and these layers can be preimpregnated and possibly laminated.
In the case of such apparatuses, a high pressure fluid jet, concentrated by a nozzle, cuts materials placed on a work table, the fluids used generally being running water. This fluid jet moves along its axis at supersonic speed at the nozzle outlet and above the members to be cut, the cutting speed being variable as a function of the materials, but can be very high. In such apparatus, the fluid jet contains a considerable residual energy on leaving the material which it has just cut. It is therefore necessary to provide a jet recovery system facing the nozzle.
Various fluid jet cutting apparatuses incorporating a jet recovery system are known.
Thus, French Pat. No. 2 405 116 describes a fluid jet cutting apparatus, which comprises a cutting table constituted by a rectangular tank, in which is mounted a bench or frame formed by a honeycomb structure and the material to be cut entirely rests thereon. The upper edges of the walls of the relatively small cells formed by the honeycomb structure are in the form of notches or scallops and have points located at the intersections of the walls of the cells and on which rests the material to be cut. Below the honeycomb structure are fixed parallel deflecting plates arranged in such a way that they are inclined downwards and their upper edges are in the form of a knife blade and located between two walls of cells of the honeycomb structure.
In this known apparatus, the recovery of the residual energy of the fluid jets takes place both by means of the points, the notches or the scallops of the honeycomb structure, which split up or fuse the jet, and by means of the relatively small cells of this structure which confine the jet. Moreover, a protective sheet made from a plastic or similar material is positioned between the material to be cut and the top of the table. This sheet, which is cut during the passage of the jet, makes it possible to prevent splashes.
According to a constructional variant of the cutting apparatus described in French Pat. No. 2 405 116, the bench or frame located in the rectangular tank no longer contains a honeycomb structure. Instead it contains a series of plates, whose upper edges are shaped like a knife blade and said plates are curved downwards and shatter the residual jet. In the upper part of the rectangular tank is placed a material such as metal wool, steel shot or grit, which serves to reduce splashes, reduce noise and prevent excessive wear to the plates. In order to absorb the residual energy, the bench contains a liquid which can be kept at a constant level.
French Pat. No. 2 405 117 describes a fluid jet cutting apparatus of the same type as in the preceding patent and applied to the cutting of a pile of flexible sheets. This apparatus comprises a cutting table formed by a basic container containing vertical elongated elements which terminate in a tip or point and on which rests the pile of sheets. A vacuum device is placed on the cutting table and applied to the periphery of the pile in such a way as to compress the latter in the vertical direction under the effect of the thus produced vacuum. The pile of flexible sheets then offers the characteristics of a rigid mass, which can be very effectively cut. In this apparatus, the residual energy is recovered by means of elongated, pointed elements and by the pressurization of the bottom of the bench or frame. As in the case of the previously described apparatus, splashes are obviated by the arrangement of polyethylene sheets between the sheets to be cut and the top of the table.
In a constructional variant of the apparatus described in French Pat. No. 2 405 117, at the bottom of the elongated, pointed elements is arranged a mass of tangled metal wires, which serve to absorb the energy. This absorption can be increased by filling the bench with a liquid in which said metal mass is immersed.
The jet recovery systems used in these fluid jet cutting apparatuses according to the prior art suffer from a certain number of disadvantages.
Thus, in these cutting apparatuses, the honeycomb structure or the like constitutes the support for the material to be cut. It is therefore necessary to have a large quantity of said structure. Moreover, the structure must be machined at least at the level of the upper edge and must frequently be replaced, because it deteriorates when used. Thus, these known apparatuses suffer from a high price and high maintenance costs.
In addition, due to the fact that the material to be cut rests directly on the honeycomb structure, serious splashes occur and protection must be obtained against these by arranging intermediate sheets between the material to be cut and the structure. These jet splashes lead to a serious wetting of the material so that its mechanical and physical properties may deteriorate.
Finally, the vacuum device used in the apparatus described in French Pat. No. 2 405 117 in order to greatly compress the stack of sheets to be cut suffers from the major disadvantage of causing serious wetting between these different stacked sheets, due to the suction of cutting water through the stack.